This invention relates generally to printer ribbon cartridges used for impact computer printers, e.g., daisy wheel or dot matrix printers, and generally to a re-inking device for ribbon cartridges.
Printer ribbon cartridges are typically provided as a disposable product including a given length of pre-inked ribbon. The length of the ribbon defines the useable life of such printer cartridges. Often the usable life is a short life resulting in frequent user dissatisfaction caused by the inability to print long documents without the fading of printed characters, or caused by the necessity of frequent cartridge replacement. It is estimated that up to 26 million impact printers are now in the hands of personal, business, government and military users in the United States alone, with up to 2 million such printers sold annually. Given the vast number of such printers in use, it may be appreciated that ribbon cartridges may be improved by providing a longer cartridge life.
Typical ribbon cartridges include a nylon ribbon, 4 to 5 mils (thousands of an inch) thick, pre-inked at manufacture to a given standard saturation level, typically between 17 and 25 percent. The ribbons are arranged as an endless loop, typically between 5 and 160 feet in length. In basic operation, the ribbon is moved past an exposed portion of the cartridge for impact by the printer head on one side and contact with paper on the other side to form a printed character upon the paper. The cartridge typically includes a mechanical input driven by the printer in order to circulate the ribbon through the cartridge. A good portion of the ribbon is collected within a pocket of the cartridge in generally serpentine configuration. As the cartridge operates, the ribbon is pushed into and drawn from the pocket. Such ribbon cartridges produce good density print when new, but gradually fade during their life span. Such cartridge life spans average 150 pages in the smaller cartridges and up to 300 pages in the larger cartridges. For very long documents, e.g., a doctoral dissertation, an inventory printout, or a book manuscript, printing with a single cartridge can result in significant fading of the printed characters. This fading of characters is apparent by flipping through the pages of the document. Such presentation is undesirable in most instances, especially in formal presentations.
Many attempts have been made to solve such fading problems and associated limited cartridge life problems. Most notable is the separate or external re-inking device which requires ribbon cartridge removal from the printer and mounting of the cartridge upon the separate re-inking device. The re-inking device turns the ribbon through the cartridge and applies a reasonably uniform distribution of ink upon the cartridge. Thus, the external re-inking device includes some mechanical coupling to the printer cartridge in order to draw the ribbon through the cartridge and access the exposed portion in a manner similar to that conducted by the printer, but for the purpose of ink delivery to the cartridge. As may be appreciated, re-inking a cartridge by use of such a separate re-inking device necessarily requires that the ribbon cartridge be taken out of use during re-inking and that sufficient time be allotted to dismount the cartridge from the printer, mount the cartridge to the re-inking device, monitor the re-inking operation, and then re-mount the ribbon cartridge upon the printer for further use. Also, in mounting the cartridge upon the re-inking device the user must thread the ribbon through the re-inking components of the device and must often wear gloves to keep the ink free of their hands.
In other approaches to the problem of limited ribbon cartridge life and ink supply, a re-inking device has been provided as in integral part of the printer cartridge. This has been done b employing a square or rectangular felt or open celled foam rubber pad with a short wick to draw the ink, by capillary action, from the pad onto a roller or gear of the cartridge, which in turn transfers ink onto the passing ribbon. The pad arrangement, however, must be inked to near saturation before the capillary action takes place, and the particulant in the ink causes the cells of the rubber or the passageways of the felt to partially clog. Thus, capillary action alone is insufficient to do the job of delivering ink to the ribbon, and this pad arrangement does not provide any force to feed ink toward the ribbon. Thus, when inked heavily enough to operate properly, such pad arrangement frequently results in ink gravitating toward the passive or active drive gear holes of the cartridge panels and ink undesirably leaks from the cartridge.
U.S. Pat. No. 2,743,470 issued to R. G. Horowitz shows for a typewriter ribbon a cylindric inking pad fed by replenishing ink from a screw-off cap on the top of the device. Such a device, wherein the ribbon enters and leaves this cylinder through two slits and passes against this inked pad, creates the problem of imparting excessive ink against the ribbon if the device is left inside the typewriter, or if the ribbon is stopped while remaining in contact with the pad. It appears that the Horowitz device was designed to be held in place by the operator while the ribbon is manually wound from the feed-spool onto the take-up spool. U.S. Pat. No. 2,441,973 illustrates a device similar to the Horowitz device, with the same deficiencies.
U.S. Pat. No. 3,951,253 shows a self-contained re-inking device designed to attach to a typewriter ribbon spool and to ink the two separate bands on a two color typewriter ribbon. The disclosure of U.S. Pat. No. 3,951,253 shows no provision for preventing excess ink delivery to the ribbon when the ribbon is not in motion. This design would produce what is known as "hot spotting" where the ribbon is overly inked in certain portions and produces non-uniform printing density.
As may be appreciated, a limited life for ribbon cartridges provides an active market for ribbon cartridge manufacturers, but is a source of frustration for users of printer cartridges. More particularly, because the nylon ribbon of most ribbon cartridges is durable enough to withstand 4 or 5 times more printing impact than the supply of ink provided in the ribbon, the ribbon cartridges lack but one component to greatly extend their useful life. It is desirable therefore, that such pre-existing ribbon cartridges be provided with a mechanism for re-inking the ribbon in order to extend the useable life of the cartridge and maintain uniform print density, but not require significant activity on the part of the user in re-inking the cartridge.